Many yaw-rate sensors are based on the use of the Coriolis effect as a measuring principle. The Coriolis force occurs when a body of mass m moves at velocity v, and a rate of rotation Ω acts in a direction perpendicular to the direction of movement, whereFcoriolis=2mvxΩ.
One option for setting a weight into motion is to excite it into oscillation, the driving oscillation.
If a rate of rotation acts on the oscillating weight, then the Coriolis forces cause it to react with a Coriolis oscillation perpendicular to the driving oscillation. If the mechanism is combined with electronics to form an oscillating circuit, then a resonator is formed, and the frequency of this driving oscillation corresponds to the resonant driving frequency of the mechanism. In the related art, these electronics are analog.
A rotation-rate sensor that functions according to this principle is described in the document “PA Low Cost Angular Rate Sensor in Si-Surface Micromachining Technology for Automotive Applications” by A. Thomae, R. Schellin, M. Lang, W. Bauer, J. Morhaupt, G. Bischopink, L. Tanten, H. Baumann, H. Emmerich, S. Pinter, J. Marek, K. Funk, G. Lorenz, R. Neul; SAE, 1999. In this microsystem, a deflection of the movable sensor weight causes a change in capacitance at micromechanical detection electrodes. These changes in capacitance are measured by analog electronics. A voltage generated by an analog controller is applied to further electrodes at the sensor element, the driving electrodes. This voltage generates an electrostatic force in the sensor element. When the periodic driving force is in suitable phase relation to the oscillation of the movable weight measured via the detection electrodes, the driving oscillation occurs at an amplitude controlled by the controller. When the supply voltage of this microsystem is switched on, it must be assumed that the movable weight of the sensor element is at rest. Since the electronics of the described system are completely analog, i.e., continuous-value, this system can start oscillating out of the noise, at the resonant frequency of the sensor element, in a manner similar to a quartz oscillator.